I will buy it again. Thank you so much for the excellent communication with the seller and his understanding. The product works perfectly as described

Shipped in a simple letter envelope, the 5 mm LED was sticking it's nose out of it on arrival. Fortunately the board did not get lost. Included was a snippet of documentation, but the simplicity of the setup does not require more.

The price seems to be a bit detached, so you either must be a millionaire (I am not) or take out a loan (I did ;-).

Now the good news for all the millionaires and overindepted: This harvester is working surprisingly well. With my forehead on the hot side of the recommended Peltier element and a sufficiently sized aluminium heat sink on the other, the tightly-focused LED is bright enough for reading a book or walking in a completely dark room.

And yes, you need to be a fast reader or fast walker: I am using the specified Peltier and a 42,5x42,5x30 mm3 heat sink taken from an old PC. The Peltier is starting at some 55 mV which makes the LED smile. After about 3 minutes the peltier is down to some 35 mV and the LED is falling asleep. Geting rid of the heat transfered first to the heat sink and then to the ambient at a heat sink to ambient temperatur difference of body temperature minus ambient seems to be challenging without a ventilator.

Maybe taking an massive block of material (aluminium at 897 J per kg per K, more than twice as goot as the heavier copper) or water at a whooping 4'200 J per kg per K) may increase your chance to read at least the preface or find the exit door into bright sunlight.

Update 7 June 2020:

I obtained a die-cast aluminium enclosure (www.gainta.com.tw, type G101-IP67, 50x45x30 mm3, available on ebay) and designed and 3D-printed a forehead-mount. Then I filled the enclosure with water up to 80% of its volume and let it rest in my freezer for some time (water will expand when freezing!). After final assembly I mounted the complete lamp on my forehead with a Velcro and ... oh boy! The LED was shining very bright and ... my forhead felt like in an arctic storm. I haven't performed any operating time evaluation yet, but from the point of view of classical physics it should work until the ice will have melted away and the water and encloure will have come up to above room temperature. So the LED may shine for a long time. Or at least as long as I can stand the arctic storm.

Update 8 June 2020:

I tamed the arctic storm with a thin (0.3 mm) sheet of cardboard between the Peltier and my forehead. After about an hour the ice had melted and the LED was getting dimmer. However there was sufficient light for about another half hour to read a book in complete darkness.

Update 28 October 2020:

I published my 3D-printable enclosure on thingiverse:
https://www.thingiverse.com/thing:4635786